A preamble is an introductory and expressionary statement in a document that explains the document's purpose and underlying philosophy. When applied to the opening paragraphs of a statute, it may recite historical facts pertinent to the subject of the statute. It is distinct from the long title

Long title

The long title is the formal title appearing at the head of a statute or other legislative instrument...

 or enacting formula of a law.
While preambles may be regarded as unimportant introductory matter, their words may have effects that may not have been foreseen by their drafters.